1. Field of the Invention
The present invention relates to a method for producing an L-amino acid such as L-glutamic acid using a microorganism. L-Glutamic acid is useful as an ingredient of seasonings, and the other L-amino acids are useful in industry as animal feed additives, health food ingredients, amino acid infusions, and the like.
2. Brief Description of the Related Art
Methods for producing a target substance such as an L-amino acid by fermentation using a bacterium can include methods of using a wild-type bacterium (wild-type strain), an auxotrophic strain derived from a wild-type strain, a metabolic regulation mutant strain derived from a wild-type strain as a strain resistant to various drugs, a strain having properties of both auxotrophic strain and metabolic regulation mutant, and the like.
For example, L-glutamic acid can be produced by fermentation using an L-glutamic acid-producing bacterium of the so-called coryneform bacterium belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or a mutant strain thereof (refer to Kunihiko Akashi, et. al. “Amino Acid Fermentation”, Gakkai Shuppan Center, 1986, pp. 195-215). Moreover, as methods for producing L-glutamic acid using other strains, methods utilizing a microorganism belonging to the genus Bacillus, Streptomyces, Penicillium, or the like (refer to U.S. Pat. No. 3,220,929), Pseudomonas, Arthrobacter, Serratia, Candida, or the like (refer to U.S. Pat. No. 3,563,857), Bacillus, Pseudomonas, Serratia, Aerobacter aerogenes (currently Enterobacter aerogenes), or the like (refer to, Japanese Patent Publication (Kokoku) No. S32-9393), a mutant strain of Escherichia coli (refer to Japanese Patent Laid-open (Kokai) No. H5-244970), and the like are known. Furthermore, the inventors of the present invention proposed a method of producing L-glutamic acid using a microorganism belonging to the genus Klebsiella, Erwinia, Pantoea, or Enterobacter (refer to Japanese Patent Laid-open Nos. 2000-106869, 2000-189169 and 2000-189175).
In recent years, recombinant DNA techniques have been used in the production of target substances by fermentation. For example, L-amino acid productivity of a bacterium can be improved by enhancing expression of a gene encoding an L-amino acid biosynthetic enzyme (U.S. Pat. Nos. 5,168,056 and 5,776,736), or by enhancing uptake of a carbon source to the L-amino acid biosynthesis system (U.S. Pat. No. 5,906,925).
For example, as for L-glutamic acid production, it was reported that introduction of a gene encoding citrate synthase from Escherichia coli or Corynebacterium glutamicum was effective for enhancement of L-glutamic acid-producing ability in a coryneform bacterium belonging to the genus Corynebacterium or Brevibacterium (refer to Japanese Patent Laid-open No. H7-121228). Furthermore, it was reported that introduction of a citrate synthase gene from a coryneform bacterium into an enterobacterium belonging to the genus Enterobacter, Klebsiella, Serratia, Erwinia or Escherichia was effective for enhancement of L-glutamic acid-producing ability (refer to Japanese Patent Laid-open No. 2000-189175).
It is also known that microorganisms which are deficient in α-ketoglutarate dehydrogenase (α-KGDH) produce a marked amount of L-glutamic acid (EP771879 A, EP0952221 A, EP1078989 A).
Succinate dehydrogenase (SDH) is an enzyme which catalyzes the reaction of converting succinic acid to fumaric acid, and it was reported that a coryneform bacterium deficient in the gene of this enzyme produced a small amount of L-glutamic acid (EP1106684 A).
Furthermore, although a succinate dehydrogenase-deficient strain is also known for Escherichia coli belonging to the enterobacteria (J. Gen. Microbiol., 1978 July; 107 (1): 1-13), the relationship between succinate dehydrogenase deficiency and L-glutamic acid production has not been previously reported.
Furthermore, it is known that if α-ketoglutarate dehydrogenase is deleted in an Escherichia coli strain, the strain becomes succinic acid auxotrophic, but the double deficiency of SDH and α-ketoglutarate dehydrogenase causes the strain to recover from the succinic acid auxotrophy (J. Gen. Microbiol., 1978 July; 107 (1): 1-13). However, the effect of the double deficiency of α-ketoglutarate dehydrogenase and succinate dehydrogenase on production of an L-amino acid such as L-glutamic acid is not known.